The theme of this application is the comparative study of auditory (including all of the octavolateralis systems) processing of complex sounds. the key elements of the research theme are the comparative approach, auditory processing, and complex sounds. The comparative approach refers to the investigators' use of different techniques (anatomy, physiology, and animal and human behavior/psychophysics), different animal models (fish, chinchilla, and humans), and different hair cell systems (auditory, vestibular, and mechanoreceptive lateral line) to understand auditory processing. Auditory processing refers to the auditory system's ability to use the biologically relevant information in sound. Since most biologically relevant sounds are complex, the auditory processing of complex sounds is a major focus of the proposed research. The normal and impaired auditory system's ability to use sound and vibration to determine the sources of sound, especially in multi-source acoustic environments, is a major cross-cutting theme of the proposed work. Support is requested for five projects and 1 core. Project 4 proposes to study (anatomically, physiologically, and behaviorally) the mechanoreceptive lateral line system in terms of its ability to determine objects in the water field that flows past a moving fish. this research relies on past work on the lateral line system, work conducted in other laboratories on the relatively well understood electro-receptive system, and on the work on auditory processing in fish. Project 2 covers work on complex sound identification and localization by fish, both behaviorally and physiologically (at the periphery and within the central nervous system). Project 1 continues research investigating the use of interaural differences of time and level to determine and locate sound sources, especially when the interaural differences associated with those sources differ across the spectrum of the complex sound field reaching the listener. Project 6 is a continuation of recent work conducted at the Parmly Hearing Institute on the use of slow coherent temporal modulation to aid the auditory system in sound source determination. In addition to human psychophysical experiments, the project includes animal psychophysical and physiological components investigating the behavioral and physiological responses of chinchillas to complex sounds with slow temporal modulations. Project 5 continues the study of the physiological basis for processing complex sounds with strong harmonic structure, such as exists in most stimuli which are perceived as having a pitch. A stimulus of particular interest is rippled-noise and its variations (i.e., comb-filtered noise). This project involves human and animal psychophysics and peripheral and brainstem physiology. Core 9001 requests support for the subjects (both human and animals) used in the five projects.